Tail Pipes Vibrating

So I go to pick up my Black Beauty Friday night...and my tail pipes are vibrating while the engine is running. There's a V8 running next to mine and his are steady. So I tell my salesman "What's up with that??" and he begins to explain the intracasies of the V8 and the V6...BS! We had a dinner date with some friends and were not able to wait around...now I got to bring it so they investgate while it's vibrating.